1. Field of the Invention
This invention relates to a compression membrane adapted for use, for example, in a drainage machine for wringing liquid out of textile products containing liquid.
2. Description of the Prior Art
FIGS. 1 through 5 show an example of the compression section of one conventional hydroextractor. In these drawings, reference numeral 1 indicates a membrane mounted between a stopper 2 and a bell 3, which may be a rubber film for wringing water out of the washing. The stopper 2 is fixed to the inner peripheral wall of the bowl-like bell 3 through, for example, the welding process.
The bell 3 is a pressure retaining vessel for holding a pressurized water 4 within a space formed between it and the membrane 1. Reference numeral 5 indicates a conveyor belt having holes or gaps penetrating therethrough from its upper surface to its under surface, on the under side of which a drainage plate 6 is disposed. This drainage plate 6 has grooves 7 formed in its upper surface for letting liquid run therethrough, whose under side is supported by a frame 8 made of a plate or a structure having a certain strength. Reference numeral 9 indicates clamps for holding and preventing the bell 3 and the conveyor belt 5 from separating from each other, which separation would otherwise occur due to a pressure caused by a hydraulic pressure 10, and each clamp 9 is moved back to the position indicated by the two-dot chain line at the no-dehydration time.
The pressurized water 4 is a pressure water supplied, for example, from a pump not shown, which compresses the washing via the membrane 1. In addition, reference numeral 11 indicates an object to be compressed under pressurization, such as the washing; 12 the object to be compressed before pressurization; 13 the direction of the water flow at the pressurization time (FIG. 1); and 14 the direction of water flow at the negative pressure time (FIG. 2).
Describing the action of the foregoing configuration, FIG. 2 shows the state before pressurization (at the suction time). In this state, the pressurized water 4 is discharged in the direction indicated by reference numeral 14 by, for example, a pump not shown, and the membrane 1 deforms upward along the inner curved surface of the bell 3 so as to assume a convex shape, this membrane being detained at its periphery by the stopper 2.
The bell 3 can move up and down and when it is positioned at the upper position, the object 12 to be compressed having been pre-shaped in the preceding step is conveyed to below the bell 3 by the conveyor belt 5.
Thereafter, the bell 3 lowers to assume the state shown in FIG. 2, and a space 15 is left between the object 12 to be compressed and the membrane 1. Then, each clamp 9 shown in FIG. 1 is moved from the position indicated by the two-dot chain line to the position indicated by the solid line to thereby hold and secure together the frame 8 and the bell 3.
When these members are held and secured by the clamps, the water flowing in the direction 14 is switched by a passage switching unit not shown so as to flow in the direction 13, the object 12 is compressed by means of the pressurized water 4 via the membrane 1, the state shown in FIG. 1 is brought about wherein the object is pressurized, and the water wrung out passes through the holes of the conveyor belt 5 and is discharged outward through the grooves 7 of the drainage plate 6.
As shown in FIG. 3 the conventional membrane 1 is of the form of a flat plate having a hook at its periphery, and is deformed as shown in FIG. 2 as described above and stretched normally by 60-70%; thus, a good stretchable rubber exhibiting an elongation percentage of 300-700% is used. At the drainage time, as shown in FIG. 4, the membrane 1 is deformed so as to conform to the object 12 to be compressed to thereby perform drainage.
According to the foregoing procedure of compressing the object 12, the volume of the object is reduced and its height is decreased to less than one half the original height. However, since the pressurizing direction points downwards, the diameter of the object 12 to be compressed enlarges. For example, an initial diameter of 950 mm increases up to a size of 1000-1050 mm immediately after compression. At this moment, as shown in FIG. 4, pinching portions 17, 18 for pinching the object to be compressed appear at the outer peripheral portion of the membrane 1, the outer peripheral portion of the object 12 to be compressed, such as the washing, is pressed against the conveyor belt 5 by means of the membrane 1, and the volume of the object 12 to be compressed is reduced while its outer peripheral portion is kept in the locked state. Therefore, as the compression step is continued with the outer peripheral portion kept in the locked state, the membrane 1 stretches in the directions of the arrow 19 and moves in the direction of the arrow 20 (see FIG. 5); thus, there arises a fear that the washing exhibiting a slight elongation will be torn.
As shown in FIG. 3, the body portion of the conventional membrane 1 is made by material having a high stretchability into the form of a flat plate with a slight portion of its marginal portion only being made high in hardness. The ratio of that slight portion to the radius is of the order of 0%-10%. Since an outermost peripheral portion 21 only is made high in hardness, when the membrane 1 is mounted so as to assume the state shown in FIG. 5, the membrane 1 cannot come off from the stopper 2; but there appears inevitably a triangular portion 22 between the membrane 1 and the belt 5 in the vicinity of the stopper 2. As a result, the outer peripheral portion of the object 12 to be compressed tends to be locked within the triangular portion 22, and as the object 12 is compressed by the pressurized water 10 via the membrane 1 as shown in FIG. 4, a number of tears will occur in a portion indicated by 23.
In addition, as the pressure of the pressurized water is removed after completion of dehydration in the state shown in FIG. 4, the object 12 having been dehydrated expands and correspondingly pushes the membrane 1 from the inside conversely; thus, the object 12 to be compressed works so as to cut into the membrane 1. During the above action, sliding does not occur if the coefficient of surface friction of the membrane 1 is large, and the space between the membrane 1 and the object 12 to be compressed takes a negative pressure; thus, the object to be compressed is frequently kept in the fastened state to the inner surface of the membrane 1 and lifted up as it is in response to rising of the bell 3. Therefore, at the subsequent time of dehydrating a next object to be compressed, the preceding object being compressed gets on this next object; thus, the machine comes inconveniently to a stop.